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Groundwater Depletion

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What makes the desert bloom? Water!

You hear a lot about making the desert bloom. Many plants do well in the desert if they are given water. Since deserts do not have much water, groundwater is used. In many desert locations, groundwater is being pumped much faster than it is being recharged. What will happen in the future?

Human Use of Aquifers

Most land areas have aquifers beneath them. Many aquifers are used by people for freshwater. The closer to the surface an aquifer is, the easier it is to get the water. However, an aquifer close to the surface is also more likely to become polluted. Pollutants can seep down through porous rock in recharge water.

People may use the water in an aquifer faster than it is recharged. When this happens, the water table will lower. Wells may go dry. To get to the water, the well will need to be dug deeper.

As the water table lowers, the ground above the aquifer may sink. This is called subsidence . When the ground subsides, any homes or other structures built above the aquifer will be damaged. The San Joaquin Valley of California is one of the world’s major agricultural areas. So much groundwater has been pumped that the land has subsided many tens of feet.

The signs on the pole show where ground level was at different years. The subsidence is due to groundwater depletion.

The Ogallala Aquifer

One of the biggest aquifers in the world is the Ogallala aquifer. As you can see below ( Figure below ), this aquifer lies beneath parts of eight U.S. states. In some places, it is less than a meter deep. In other places, it is hundreds of meters deep. The water in the aquifer is mostly from the last ice age.

In this map, the area over the Ogallala aquifer is shaded in blue.

The Ogallala aquifer is an important source of freshwater in the American Midwest. This is a major farming area, and much of the water is used to irrigate crops. The water in this aquifer is being used up ten times faster than it is recharged. If this continues, what might happen to the Ogallala aquifer?

Vocabulary

  • subsidence : Sinking of the land surface because of the extraction of ground water.

Summary

  • When water is pumped from an aquifer, the water table goes down. Wells must be drilled deeper to get water.
  • The Ogallala Aquifer was filled in the ice age. It is heavily used to irrigate Midwestern farms. The use rate is several times faster than the recharge rate.
  • Ground subsidence is a consequences of groundwater overuse.

Practice

Use the resource below to answer the questions that follow.

  1. Where is the Ogallala aquifer found?
  2. How many states does it cover?
  3. What has put the Ogallala aquifer at risk?
  4. What is the danger from the Tar Sands pipeline?
  5. Why are people concerned about the pipeline?

Review

  1. What are some of the problems that come from overuse of groundwater?
  2. Why is the Ogallala aquifer important?
  3. Why does groundwater removal cause the ground to subside?

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